1. Field of the Invention
The present invention relates to an image reading device in which an image recorded in a film, for example, is irradiated with a light beam and the image is read using a line sensor.
2. Description of the Related Art
Conventionally, there is known an image reading device in which a film is intermittently moved along a direction perpendicular to a longitudinal direction of a line sensor, so that an image is read line by line. Namely, while the film is stopped, a light beam outputted from a light source illuminates the film, so that one line image is sensed by the line sensor. After this sensing operation, the film is moved by a predetermined amount by a moving mechanism. The sensing operation and the movement are repeatedly carried out, so that one frame image is read.
A black level correction data is subtracted from one line of pixel data outputted from the line sensor, and then the black-level-corrected pixel data is multiplied by a white level correction coefficient, so that the black-level-corrected pixel data is further subjected to a shading correction. The white level correction coefficient is used for correcting an error generated mainly due to an unevenness in the radiation of light from the light source, and is obtained when the power source is turned on prior to loading a film on the image reading device.
One line of pixel data, having been subjected to the black level correction and the shading correction, is then multiplied by a color correction coefficient, so that a balance among the red, green and blue components of the image is adjusted. The color correction coefficient is calculated based on image data obtained by an exposure measurement performed prior to reading operations (i.e. a pre-scanning operation and a regular scanning operation) of the image, and is obtained whenever the image to be read is changed. For example, when six images recorded on one film are read, the color correction coefficient is obtained six times, while the white level correction coefficient may be obtained once, or may be obtained when a film holder, in which the film is held, is removed from the image reading device or retracted from a reading optical path through which the light beam passes.
Thus, the white level correction coefficient and the color correction coefficient are calculated under independent conditions, and in an image process, these coefficients are separately applied to one line of pixel data as the one line of pixel data is outputted from the line sensor. Therefore, a problem occurs in a conventional device wherein the required image-processing time is relatively long.